In the electrophotographic image forming method, an image is usually formed on a transferring sheet according to the following processes. Namely, an electrified toner is supplied onto an electrostatic latent image formed on an electrostatic latent image carrier typically an electrophotographic photoreceptor by contacting or non-contacting method for developing the electrostatic latent image to form a visible image, and the resultant toner image formed on the electrostatic latent image carrier is transferred onto paper and then fixed to form a final image.
The developing method for forming the toner image on the electrostatic latent image carrier includes a double-component developing method using a double-component developer and a single-component developing method using a single-component developer singly composed of a toner. In the single-component developing system, carrier is not used and the toner is charged by rubbing and pressing with an electrifying member or the surface of a developing roller. Therefore, such the method has a merit that the structure of the developing device can be simplified and made compact. Particularly, the image formation by the non-magnetic single-components developing system is influential to full color image forming apparatus corresponding to colorization of toner image, in which plural developing devices such as those for yellow, magenta, yellow and black toners have to be arranged in a limited space. Moreover, full color pictorial image can be formed by the use of polymerized toner which can be produced while controlling the size and the shape of the toner particle in the course of the production process; cf. Patent Document 1, for example.
The developing roller to be used for image formation by the non-magnetic single-component developing system, for example, has a constitution in which a resin layer is placed on a rubber layer provided on the circumstance of a shaft, and a thin layer of toner is formed on the developing roller by a metal plate or a roller. The thin layer of toner is electrified by the friction with the above metal plate or the roller.
The resin layer formed on the surface of the developing roller is required to stably donate electricity to the toner and to suitably convey the toner, and technology for preventing the adhesion or fusion of the toner onto the developing roller surface is investigated hitherto. For example, use of a fluororesin and improving the properties thereof has been tried.
Moreover, improvement in the durability by a means such as formation of strong contact between the resin layer and the rubber layer has been demanded since large load is applied not only to the toner but also to the developing roller on the occasion of the formation of the toner thin layer performed on the developing roller surface. Consequently, a developing roller improved in the durability by forming an inter layer formed by employing a silane coupling agent and further forming thereon a resin layer principally composed of fluororesin is disclosed. The inter layer is also called an adhesive layer because of its purpose of adhesion. Cf. Patent Document 2, for example.
Patent Document 1: Japanese Patent Open to Public Publication (JP A) No. 2000-214629
Patent Document 2: Japanese Patent Open to Public Publication (JP A) No. 8-190263